Method of preparing foam from a milk-based alimentary liquid and method for implementing the same

ABSTRACT

The invention concerns a method for preparing foam from a milk-based alimentary liquid, including the successive steps of: a) spacing a quantity of alimentary liquid in a container associated with stirring members; b) heating said quantity of alimentary liquid to bring it in proximity to a first desired temperature level while mechanically stirring it at a first stirring speed, lower than the foam creating speed, and c) stirring said quantity of liquid at a second stirring speed, sufficient to make said liquid foam.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/598,669, filed Jun. 19, 2007, which is the U.S. national stagedesignation of International Application No. PCT/EP05/002378 filed Mar.7, 2005, which claims priority to EP 04005729.1 filed on Mar. 10, 2004,the entire contents of which are expressly incorporated herein byreference.

BACKGROUND

The present invention concerns a method of preparing foam or froth froma milk-based alimentary liquid, intended for example, to be used in thepreparation of coffee-based drinks such as cappuccinos, milky coffee,café latte and macchiato, etc. The present invention also concerns adevice for implementing said preparation method.

Currently, the most common method of preparing foam from a liquid suchas milk is to pour the desired quantity of milk into a receptacle, todip the steam outlet nozzle of a coffee machine into the receptaclewhile shaking it from top to bottom to draw in the air necessary toobtain foam.

A first drawback of this method is the need to have either aprofessional type coffee machine which is generally expensive, or adomestic coffee machine with a steam outlet nozzle which is generallyinappropriate.

Another drawback lies in the fact that it is not generally possible toprepare the foam at the same time as the coffee, unless one has acomplex and expensive coffee machine with fluid systems for producinghot water for the coffee and for producing steam that are independent ofeach other.

Another drawback linked to the use of coffee machines with a steamoutlet nozzle arises from the fact that the water heating system in suchmachines, usually a heating-unit, has to remain permanently switched onin order to be kept at a high temperature and to be able to producesteam without requiring inconvenient waiting time. These coffee machinesconsequently consume significant quantities of energy, which makes theuse thereof uneconomical. It should also be noted that depending uponthe hardness of the water used, the steam flow nozzles quickly becomecoated with limescale so that the machines have to be regularly takenout of service in order to descale them.

Another drawback of this type of machine arises from the fact that thequality of the foam obtained depends upon the skill of the user suchthat the machines do not allow foam with homogenous consistence andquality to be obtained in a reproducible manner.

Household appliances for stirring alimentary liquid in order to generatefoam using mechanical elements are already known. However, the operationmode of these devices is too general and not adapted for generating asmooth, fine and hot milk foam in a very short period of time in orderto prepare a drink such as a cappuccino. The use of these devices isalso not very practical or very hygienic. Indeed, the stirring elementsneed to removed to be cleaned which requires some handling by the user.The stirring elements can also dirty the rest of the device when it isdismantled particularly the heating element with all the drawbackslinked with cleaning burnt on food residue. All these drawbacks makethem inconvenient to use for preparing foam based drinks.

SUMMARY

It is thus a main object of the invention to overcome the drawbacks ofthe aforementioned prior art by providing a method of preparing foamfrom a milk-based alimentary liquid that is simple, economical, and easyto use and that produces rapidly high quality foam in a reproduciblemanner.

It is also an object of the invention to provide a device forimplementing such a method.

It is also an object of the invention to provide a device of this typewhich can easily and quickly used, that further requires minimummaintenance and that can be easily cleaned after use.

It is also an object of the invention to provide a device of this typefor producing foam from a milk-based alimentary liquid that does notrequire the use of steam.

It is also an object of the invention to provide a device of this typethe implementation of which for producing foam can easily be automated.

It is also an object of the invention to provide a device of this typeindependent of a conventional coffee machine.

The invention thus concerns a method of preparing foam from a milk-basedalimentary liquid for preparing a drink such as a cappuccino with adevice comprising a frame including a support for a container, saidsupport being associated with heating means for heating said alimentaryliquid contained in said container when the container is disposed onsaid support, mechanical stirring means extending at least partiallyinto said container, means for driving said stirring means, and controland command means arranged for automatically controlling the command ofsaid heating means and said drive means, said method comprising thesuccessive steps of:

-   -   a) placing a quantity of alimentary liquid in the container        associated with said stirring means;    -   b) commanding, via the control and command means said heating        means associated with said support for heating said quantity of        alimentary liquid and bring it in proximity to or at a        predetermined temperature level while commanding said driving        means for said mechanical stirring means at a first        predetermined stirring speed, lower than the foam generating        speed for stirring said quantity of alimentary liquid; and    -   c) commanding, via the control and command means said mechanical        stirring means for stirring said quantity of liquid at a second        predetermined stirring speed, effective to make said liquid        foam.

This method advantageously enables foam to be prepared quickly, i.e.within few seconds only, from a determined quantity of liquid using amechanical stirring device of simple and economical construction thatdoes not use steam; thereby removing the drawbacks associated with theproduction of steam. Since the device for implementing this method canbe made separately from a coffee machine, it is possible to prepare thecoffee and the foam simultaneously.

Preferably, the quantity of heating energy used during step b) isadapted as a function of said quantity of liquid to be made to foam,such adaptation of the quantity of heating energy can be achieved byadjusting the heating power and/or the heating time.

It will be noted that simultaneously stirring and heating the liquid atthe speed lower than the foam generating speed, typically of the orderof 500 to 1500 rpm, brings the entire volume of liquid to the optimumfoam forming temperature more quickly. Of course, the foam generatingspeed can vary depending upon the propensity of the alimentary liquid toform foam, depending, in particular, upon its composition, such as itsfat, emulsifier, water and/or protein content.

Since foam is a thermal insulator which could slow down the temperatureincrease of the liquid, it is thus important to ensure that foam doesnot form before the liquid has reached the optimum foam formingtemperature, typically comprised between 60° C. and 70° C. in the caseof milk.

Preferably, the second predetermined speed is at least twice, preferablythree times higher than the first predetermined speed. The firstpredetermined speed range is chosen so that a forced convection mode iscarried out in the liquid which promotes a more rapid rise oftemperature in the liquid but is still low enough to not form foam whichwould act as a thermal insulator. The second predetermined speed rangeis selected so that the liquid which has substantially reached itstemperature level can be changed rapidly into a foam.

According to a preferred embodiment of the invention, the liquid is keptat the determined temperature during the foam forming step in order tooptimise formation of the foam and to be able to use “hot” foamthereafter.

Moreover, it will be noted that during the foam forming step, thestirring is advantageously carried out in a discontinuous manner inorder to reduce the time for converting the liquid into foam. Suchstirring is advantageously achieved using a rotating stirring memberrotating at a high speed during step c), typically between 3000 and10000 rpm. Indeed, it has been observed that at these speeds, the foaminitially formed is quickly pushed via centrifugal force against thewalls of the container, thus moving away from the stirring member, sothat a significant part of the foam is no longer being stirred. In orderto overcome this problem, the stirring is discontinuous in order toregularly interrupt the aforementioned centrifugal effect. These regularinterruptions, which preferably have a frequency of the order of 0.3 to0.5 Hz, thus enable the foam to descend again and come into contact withthe rotating stirring member to be stirred again as soon as stirringbegins again. It will be noted in this regard that the rotating stirringcan start again in the same rotational direction or in the oppositedirection. By way of indication, the foam forming step lasts around 5 to15 seconds for a volume of liquid of 40 to 80 milliliters.

According to another aspect, the invention concerns a device forpreparing foam from a milk-based alimentary liquid for preparing a drinksuch as a cappuccino, including a container for receiving saidalimentary liquid, a frame including a support for said container, saidsupport being associated with heating means for heating said alimentaryliquid contained in said container when the container is disposed onsaid support, stirring means extending at least partially into saidcontainer, means for driving said stirring means, and control meansarranged for controlling said heating means and said drive means,characterized in that said frame is connected to a mobile coverextending above said container, in that said drive means are disposed insaid cover and in that said cover is mobile between a first position inwhich said drive means are coupled to said stirring means and a secondposition in which said drive means are uncoupled from said stirringmeans.

The principle of connecting the driving means to the stirring means asdefined allows the device to be maintained more hygienically inparticular by keeping the stirring means in the container after usewhich prevents the liquid or foam dripping onto the heating element andthus dirtying the latter or giving off undesirable burning odours. Thestirring means can thus be cleaned more easily. Coupling is also quickerand the device is thus more convenient to use.

According to a preferred embodiment, the control means are arranged forheating a quantity of liquid for bringing it in proximity to a desiredtemperature level while stirring said quantity of liquid at a firstspeed during a first phase and for stirring said quantity of liquid at asecond speed higher than said first speed during a second phase, andcomprise selection means for adapting the quantity of heating energyprovided during the first phase as a function of said quantity ofliquid.

Thus, it is possible to automatically programme the duration of thefirst and second stirring periods and the passage from one period toanother; in addition to the frequency of interruption and changes ofdirection. Such programming can occur by storing a programme using amicrocontroller as a function of the capacity of the container. When thecontainer is provided for one or two cups, it is quite easy toanticipate in advance the duration, rotation and frequency settings forthe proper temperature and proper foaming of the liquid without havingto use a temperature regulation. These production programmes or cyclescan simply be switched on by actuating control keys associatedrespectively with predefined volumes of liquid to be foamed.

In addition to the heating time control, control of the stirring time ata first speed and control of the stirring time at a second speed, whererotating stirring means are used, the control means can advantageouslycontrol both the change of rotational direction of the latter and thefrequency of such changes.

The container is advantageously removable and is associated with a covercarrying the stirring means. Those elements coming into contact with thealimentary liquid can thus be provided in dishwasher proof materials andare thus easy to clean. According to another embodiment of theinvention, the device includes temperature detection means and thecontrol and management means are arranged for controlling said drivingmeans at least two speed levels as a function of the temperature leveldetected.

Other features and advantages of the invention will appear upon readingthe description of an example embodiment, given by way of non-limitingillustration, with reference to the annexed drawings, in which:

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a general perspective view of a device for preparing foam inaccordance with the invention, and

FIGS. 2 and 3 are cross-sectional views of the device for preparing foamin accordance with the invention shown respectively in the operatingposition and in the rest position.

DETAILED DESCRIPTION

Referring to FIGS. 1 to 3, there is shown a device according to theinvention for preparing foam from a milk-based alimentary liquiddesignated by the general reference numeral 1. Device 1 includes acontainer 2 for receiving an alimentary liquid, typically milk, fromwhich the foam will be produced. In the example illustrated, container 2has the form of a generally cylindrical pot with a slightly flaredportion provided with a beak (not shown). Container 2 can be made of anymaterial withstanding temperatures of the order of 200° C. for examplePyrex glass or similar. Other geometrical shapes can of course beenvisaged for the container. It will be noted that in this exampleembodiment, container 2 includes three level markers 2 a, 2 b, and 2 cfor determining three filling levels of container 2. A handle (notshown) secured to the container, for example by a metal binding can beenvisaged to facilitate handling thereof.

The device further includes a frame 4 provided with a support 6 having asurface 6 a of substantially complementary dimensions and shapes to thebottom surface of container 2 for receiving and positioning the latter.For this purpose, the surface of support 6 a is arranged to be slightlyset back in relation to the upper surface of support 6. Container 2 isthus removably mounted on support 6 of frame 4. The surface 6 a ofsupport 6 is in a thermal relationship with an electrical heatingelement 8 for heating the alimentary liquid contained in container 2.Heating element 8 is, for example, formed of a resistant heating plateor a halogen lamp. In the latter case, it will be noted that the supportsurface 6 a is formed of a vitroceramic plate underneath which thehalogen lamp is arranged. It goes without saying that any other type ofelectrical heating body can be envisaged. The heating element hassufficient power to quickly heat a quantity of alimentary liquid from 40ml to 80 ml to a temperature comprised between 60° and 85° C., forexample with power comprised between 600 and 2300 W.

Device 1 further includes mechanical stirring means 10 which extend atleast partially into container 2. Stirring means 10 are of the rotatingtype and comprise a rod 10 a provided, at its distal end, with astirring head 10 b which extends in proximity to the bottom of container2. Typically, stirring head 10 b includes a ring-shaped helical spring.According to a variant that is not shown, the stirring head can includea plurality of radial and vertical wings. The Figures also show that inthis example, rod 10 a includes a collar 10 c arranged at approximatelymid-length. Collar 10 c advantageously enables liquid dripping down fromthe stirring head to be recovered when the cover is removed fromcontainer 2 and rests flat on its upper surface.

In this example embodiment, it can be seen that container 2 isassociated with a cover 12 which carries stirring means 10. Morespecifically, rod 10 a is rotatably mounted via its proximal end incover 12. The end of rod 10 a passes through the cover to extend outsidethe container when the cover closes the latter. This end includes afemale coupling part 14 for cooperating with a complementary malecoupling part 16 connected to means 18 for driving stirring means 10.Advantageously, coupling with the driving means is achieved via frictionfor example of the cone on cone type.

Drive means 18 are typically made in the form of an electrical motorwith two directions of rotation capable of rotating within ranges ofspeed from 500 to 10000 rpm. These drive means 18 are mounted in amobile cover 20 connected to frame 4 and extending above container 2.Cover 20 is mounted so as to be mobile on frame 4 so that it can pivotbetween a first position (FIG. 2) in which drive means 18 are coupled tostirring means 10 and a second position (FIG. 3) in which said drivemeans are uncoupled from stirring means 10 and in which container 2 canbe removed from device 1.

It will be noted in this regard that the cover is associated withlocking means 22 provided for holding cover 20 respectively in the firstand second positions. Locking means 22 have here the shape of anarticulated hook 22 a secured to cover 20 cooperating with a pin 22 bsecured to frame 4. Hook 22 a can be actuated for locking and/orunlocking via a toggle mechanism 23, one lever 23 a of which isconnected to hook 22 a and the other lever 23 b of which is connected toa control member accessible from the outside of cover 4, lever 23 bresting on pin 23 c secured to the cover.

Device 2 further includes control means 24 disposed in frame 4 andarranged for managing the control of heating body 8 and drive means 18.More specifically, the control means are arranged for heating a quantityof liquid to bring it in proximity to a desired temperature level whilestirring said quantity of liquid at a first speed during a first phaseand for stirring said quantity of liquid at a second speed higher thanthe first speed during a second phase. Since the heating and stirringconditions of the alimentary liquid depend upon the quantity ofalimentary liquid contained in container 2, control means 24 comprise amicrocontroller connected to motor 18 and to the heating element, andsuitably programmed for controlling one or more foam producing cycles asa function of the quantity of liquid to be foamed. Control of thesecycles is started by actuating control keys 26 a, 26 b, 26 c, each ofthe keys corresponding to control by the microprocessor of a foamproduction cycle for a determined quantity of liquid. In the exampleshown, the control keys are three in number and correspond respectivelyto switching on a foam producing cycle for the three levels of liquiddefined by the level markings 2 a, 2 b and 2 c of container 2. Thesecontrol keys 26 a, 26 b, 26 c therefore form selection means foradapting the quantity of heating energy supplied during the first phaseof the foam producing cycle and the duration of the second phase, as afunction of the quantity of liquid in container 2. The heating energycan easily be adapted either by adjusting the power and/or the heatingtime.

Typically, the two speed levels can be obtained by acting directly uponthe electrical motor control by varying the frequency of the controlsignal sent by the microcontroller. According to a variant one couldalso envisage varying the speed mechanically by varying a gear ratiodisposed between the motor output and the stirring means.

The electrical elements of device 1 are powered via a supply plug 28secured to the frame and intended to be connected to the mains supplyvia a conventional supply lead.

The method according to the invention for preparing foam from adetermined alimentary liquid, in this case milk, will now be describedusing device 1 according to the invention and illustrated in FIGS. 1 and2.

First of all a quantity of milk, corresponding to one of the threelevels marked by marking lines 2 a, 2 b and 2 c, is poured intocontainer 2. Container 2 is then closed by means of cover 12 carryingstirring means 10. Container 2 is then placed on support surface 6 a,cover 20 of device 1 having previously been placed in the open position(FIG. 2). Cover 20 is then tipped (FIG. 1). This causes male couplingpart 16 connected to the drive means to friction fit into femalecoupling part 14 secured to stirring means 10 and emerging from cover 12of container 2. Once in this configuration, control key 26 a, 26 b or 26c, corresponding to the level of liquid contained in container 2, can beactuated. Such actuation switches on the foam preparing cyclecorresponding to the level of liquid selected, this cycle beingcontrolled by control means 24.

During a first phase of the preparation cycle, control means 24respectively switch on heating element 8 and motor 18 to supply thequantity of calorific energy necessary to bring the quantity of liquidselected to a desired temperature level and to mechanically stir thequantity of liquid at a first stirring speed, lower than the foamcreating speed. Typically, the desired temperature for facilitatingformation of milk foam is of the order of 60 to 70° C. and the firststirring speed is comprised between 500 and 1500 rpm and is preferablyof the order of 800 rpm. Stirring at a relatively low speed homogenisesthe temperature of the milk in the container preventing layers ofdifferent temperatures from forming and in particular, the lowest layerfrom burning and sticking to the bottom of the container, whileactivating the desired temperature increase.

As soon as the quantity of heat energy corresponding to the quantity ofliquid selected has reached the desired value, the microcontrolleradjusts the command of heating element 8 so as to keep the quantity ofalimentary liquid at the desired temperature level and triggers entryinto a second phase during which the foam will be produced. For thispurpose, the microcontroller sends a signal to motor 18 to drive thelatter at a second stirring speed suitable for forming foam. This speedis typically comprised between 3000 and 10000 rpm and preferably of theorder of 5000 rpm. The duration of this second phase which is controlledby the microcontroller varies in accordance with the quantity of liquidselected. Typically, for a quantity of liquid from 40 to 80 ml, theduration of this second phase is of the order of 5 to 15 seconds, whichenables a foam phase to be prepared of the order of 30% to 60% foam withrespect to the liquid phase. Preferably, the microcontroller isprogrammed, during this second preparation phase, to drive stirring in adiscontinuous manner, or in other words to regularly interrupt andrestart stirring during this phase in order to optimise foam formation.Typically the interruption frequency is of the order of 0.3 to 0.5 Hz.Preferably, the microcontroller can be programmed such that stirringmember 10 changes its direction of rotation after each interruptionduring this second phase. Once the second phase has finished, themicrocontroller commands the automatic stopping of device 1. Then cover20 has only to be unlocked, tipped into its opening position andcontainer 2 containing the foam can be removed.

The invention is of course not limited to the embodiment describedhereinbefore and it will be understood that various alterations and/orimprovements evident to those skilled in the art could be made withoutdeparting from the scope of the invention defined by the annexed claims.In particular, in order to limit the centrifugation effect duringstirring, stirring means 10 could also be moved from top to bottomand/or in a transverse plane to bring the foam back into contact withthe stirring means. Second stirring means could also be used, whichdepending upon the geometry of the container, could be disposed at thesame level as the first means or at different levels. It should also benoted that the heating could be interrupted during the second foampreparing phase. Likewise, passage from a first stirring speed to asecond stirring speed in the method according to the invention can occurgradually without departing from the scope of the invention.

According to an alternative embodiment, the microcontroller can beassociated with means for detecting the temperature (not shown) of thealimentary liquid in order to command motor means 18 in accordance withat least two speed levels as a function of the temperature leveldetected. The temperature detection means typically comprise a thermalswitch associated with the heating element and which enables the latterto be switched on as soon as a predetermined desired temperature hasbeen reached. In this case the temperature of the liquid is measuredindirectly. One could also envisage arranging a temperature sensor inthe container, for example secured to the stirring means in order toobtain a direct liquid temperature measurement. According to thisvariant, the temperature detection means regularly send signalrepresentative of the temperature to the microcontroller during thefirst phase. As soon as the temperature has reached the desired value,the microcontroller commands the control of the heating element 8 so asto keep the alimentary liquid at the desired temperature and triggersentry into the second phase during which the foam will be produced, themicrocontroller then sending a signal to motor 18 to drive the latter ata second stirring speed suitable for forming foam.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The invention claimed is:
 1. A device for preparing foam from amilk-based alimentary liquid for preparing a drink, the devicecomprising: a container for receiving the alimentary liquid, a frameincluding a support for the container, the support being associated witha heater for heating the alimentary liquid contained in the containerwhen the container is disposed on the support, a stirrer extending atleast partially into the container, drive means for driving the stirrer,and control means arranged for controlling the heater and the drivemeans, the control means arranged for heating a quantity of liquid tobring the quantity of liquid in proximity to a desired temperature levelwhile stirring the quantity of liquid at a first speed during a firstphase and for stirring the quantity of liquid at a second speed during asecond phase, the control means comprising selection means for adaptingthe amount of heating energy supplied during the first phase as afunction of the quantity of liquid, the frame being connected to amobile cover extending above the container, wherein the drive means isdisposed in the cover and the cover is mobile between a first positionin which the drive means is coupled to the stirrer and a second positionin which the drive means is uncoupled from the stirrer.
 2. The deviceaccording to claim 1, wherein the second speed is higher than the firstspeed.
 3. The device according to claim 1, wherein the control means isarranged for heating the quantity of liquid during the second phase. 4.The device according to claim 1, wherein the selection means includes aplurality of control keys, each of the keys corresponding to the supplyof a quantity of energy for a determined quantity of liquid.
 5. Thedevice according to claim 1, wherein the container is removably mountedon the support.
 6. The device according to claim 1, wherein thecontainer is associated with a cover and the cover carries the stirringmeans.
 7. The device according to claim 1, wherein the stirrer is formedby a rod including a stirring head at its distal end.
 8. The deviceaccording to claim 7, wherein the rod is rotatably mounted in the cover.9. The device according to claim 7, wherein the stirring head extends inproximity to the bottom of the container.
 10. The device according toclaim 1, wherein the drive means is coupled to the stirrer by a frictioncoupling.
 11. The device according to claim 1, comprising locking meansfor holding the cover respectively in the first and second positions.12. The device according to claim 1, wherein the control means isdisposed in the frame and the control means is connected to control keysarranged on one surface of the cover.
 13. The device according to claim1, wherein the drive means further includes a motor with two directionsof rotation.
 14. A device for preparing foam from a milk-basedalimentary liquid for preparing a drink, the device comprising: acontainer for receiving the alimentary liquid, a frame including asupport for the container, the support being associated with a heaterfor heating the alimentary liquid contained in the container when thecontainer is disposed on the support, a stirrer extending at leastpartially into the container, drive means for driving the stirrer, andcontrol means arranged for controlling the heater and the drive means,wherein the control means includes temperature detection means and thecontrol means is arranged for controlling the drive means in accordancewith at least two speed levels as a function of the temperature leveldetected, and the frame is connected to a mobile cover extending abovethe container, wherein the drive means is disposed in the cover and thecover is mobile between a first position in which the drive means iscoupled to the stirrer and a second position in which the drive means isuncoupled from the stirrer.